What “Build action” settings in Visual Studio file's do?

• None: The file is not included in the project output group and is not compiled in the build process. An example is a text file that contains documentation, such as a Readme file.
• Compile: The file is compiled into the build output. This setting is used for code files.
• Content: Allows you to retrieve a file (in same dir as assembly) as a stream via Application.GetContentStream( uri ). For this method to work, it needs a AssemblyAssociatedContentFile custom attribute which VS graciously adds when you mark a file as "Content"
• Embedded resource: embeds the file in an exclusive assembly manifest resource.
• Resource (wpf only): embeds the file in a shared (by all files in the assembly with similar setting) assembly manifest resource named AppName.g.resources.
• Page (wpf only): Used to compile a xaml file into baml. The baml is then embedded with the same technique as Resource (i.e. available as `AppName.g.resources)
• ApplicationDefinition (wpf only): Mark the XAML/class file that defines your application. You specify the code-behind with the x:Class="Namespace.ClassName" and set the startup form/page with StartupUri="Window1.xaml"
• SplashScreen (wpf only): An image that is marked as SplashScreen is shown automatically when an WPF application loads, and then fades
• DesignData: Compiles xaml viewmodels so that usercontrols can be previewed with sample data in visual studio (uses mock types)
• DesignDataWithDesignTimeCreatableTypes: Compiles xaml viewmodels so that usercontrols can be previewed with sample data in visual studio (uses actual types)
• EntityDeploy: (Entity Framework): used to deploy the Entity Framework artifacts
• CodeAnalysisDictionary: A xml file containing custom word dictionary for spelling rules